Which bacteria is the causative agent of gas gangrene?

Correct Answer: C

Rationale: The correct answer is C: Clostridium perfringens. This bacterium is the causative agent of gas gangrene due to its ability to produce gas and toxins in anaerobic conditions. Clostridium tetani causes tetanus, Clostridium botulinum causes botulism, and Bacillus anthracis causes anthrax, not gas gangrene. Clostridium perfringens stands out as the correct choice based on its specific association with gas gangrene and its pathogenic mechanisms.

Correct Answer: D

Rationale: The correct answer is D: Yersinia enterocolitica. This bacterium can contaminate foods and grow at refrigerator temperatures due to its psychrotrophic nature. Yersinia enterocolitica is known to cause foodborne illnesses even when stored at cold temperatures. Shigella sonnei is a human pathogen transmitted through fecal-oral route, Campylobacter jejuni is typically found in poultry and causes food poisoning, and E. coli can cause foodborne illnesses but does not grow well at refrigerator temperatures.

Correct Answer: B

Rationale: The correct answer is B because peritrichous bacteria have flagella distributed all over their surface, allowing them to move in various directions. Choice A is incorrect because bacteria with a single flagellum at one pole are called monotrichous. Choice C is incorrect as bacteria with a single flagellum at each pole are known as amphitrichous. Choice D is incorrect because peritrichous bacteria have multiple flagella all over their surface, not limited to one or both poles.

Correct Answer: C

Rationale: The correct answer is C: ECHO virus infection. ECHO virus is transmitted via the fecal-oral route, meaning the virus is passed from feces to the mouth. This transmission occurs through contaminated food, water, or surfaces. Relapsed fever and spotted fever are generally transmitted by arthropod vectors like ticks. Pertussis, also known as whooping cough, spreads through respiratory droplets. Therefore, the fecal-oral route is not applicable to these diseases.

Correct Answer:

Rationale: Correct Answer: C: opportunists Rationale: 1. Opportunistic microorganisms cause infections only when the host's immune system is compromised. 2. They are typically harmless in healthy individuals but can become pathogenic in weakened hosts. 3. Saprophytic microorganisms are environmental decomposers, not inherently pathogenic. 4. Facultative pathogens can cause disease in both healthy and compromised hosts. 5. Obligate pathogens always cause disease regardless of the host's condition. Summary: A: Facultative pathogens can cause disease in healthy hosts. B: Saprophytes are not inherently pathogenic. D: Obligate pathogens always cause disease.

Correct Answer: D

Rationale: The correct answer is D because it encompasses the true statements regarding the laboratory diagnosis of urinary tract infections. A: Bacteriuria of less than 10^5 can be significant in treated patients due to the development of antibiotic resistance. B: Staphylococcus aureus, Salmonella typhi, and Mycobacterium tuberculosis may be significant regardless of quantity due to their pathogenic nature. C: Leukocyturia indicates inflammation, and even a lower number of leukocytes can be clinically significant. Therefore, option D covers all these aspects making it the correct choice.

Correct Answer: B

Rationale: I apologize for the confusion, but the correct answer to the question is actually A: microtubules. Microtubules are indeed shaped like hollow cylinders made out of tubulin proteins. They play a crucial role in cell structure, cell division, and intracellular transport. Microfilaments (choice B) are composed of actin proteins and are not shaped like hollow cylinders. Intermediate filaments (choice C) are more rope-like in structure and are made up of various proteins. Flagella (choice D) are whip-like structures used for cell movement and are not shaped like hollow cylinders.

Correct Answer: A

Rationale: The correct answer is A: Haemolytic streptococci. Hemolytic streptococci are known to cause serious infections in humans, including strep throat and skin infections. These bacteria have the potential to spread rapidly and cause epidemics. Bacilli are a broad category of bacteria and not all are necessarily harmful. Micrococci are commonly found on human skin and are generally harmless. Yeast fungi are also commonly found in the environment and are not typically associated with causing epidemics. Therefore, the presence of hemolytic streptococci in the air of a pharmacy indicates a direct epidemic danger due to their pathogenic nature and potential to cause widespread infections.

Correct Answer: B

Rationale: The correct answer is B: Streptococcus mutans. This bacterium is associated with the formation of dental caries due to its ability to metabolize sugars and produce acids that demineralize tooth enamel. Streptococcus pneumoniae (choice A) is not typically associated with dental caries. Bacillus anthracis (choice C) causes anthrax, not dental caries. Clostridium botulinum (choice D) causes botulism, not dental caries. Streptococcus mutans' unique characteristics make it the correct choice for the bacteria associated with dental caries.